1. Field of the Invention
The present invention is directed to a device for capturing and processing image information using a pseudo-random pixel interlace. This process permits the use of this image information by a variety of normally incompatible interfaces.
2. Related Art
There are four common frame rates used in moving imagery in the world today. In the U.S. and Japan, NTSC has a 59.94 Hz interlaced field rate. In Europe, PAL and SECAM have a 50.0 Hz interlaced field rate. The motion picture industry predominantly uses 24 frame per second film. Some High Definition Television (HDTV) proposals use 60.0 Hz interlaced fields (such as the Japanese standard developed by NHK, also called SMPTE 240M and BTA001), and some use 60.0 Hz progressively scanned images (non-interlaced) (presently under discussion in the United States). Thus 24, 50, 59.94, and 60.0 Hz are common picture frame rates in the world.
On motion picture film, 30 Hz, 60 Hz, and 72 Hz have all been used on occasion.
On computer displays, progressively scanned (noninterlaced) images are often displayed at 66 Hz (Apple Macintosh II color screen), 70 Hz, 72 Hz, 75 Hz, and 76 Hz. These CRT screen refresh rates exceed 60 Hz because the 60 Hz rate flickers excessively under fluorescent lights in bright viewing environments as found in most offices.
For covering sports, motion rates faster than 45 Hz are felt to be required.
Further, current television formats have either 240 lines per field for NTSC or 288 lines per field for European PAL. In other countries, such as those in South America, other combinations of PAL and NTSC line formats and rates are found.
With limited exceptions, these frame rates and line formats are incompatible with each other. For a single viewable event, therefore, this incompatibility makes it necessary to have a number of different corresponding video image capturing and formatting devices in order for different end-viewers to be able to view the event. Similarly, the incompatibility makes it extremely difficult to transfer information recorded in one format to another format.
For example, when moving images are captured in the U.S. in NTSC, they must be converted to European PAL for display in Europe, or to other formats. This conversion process is sometimes called "transcoding". Both the field and frame rates, as well as the number of scan lines must be converted. This transcoding conversion process is usually expensive. Worse yet, the results of transcoding are often felt to be poor, and the transcoding process is prone to aliasing artifacts and resolution degradation, as well as motion degradation.
As indicated above, some of the present-day systems use interlace as part of the video format. Interlace is a technique which is used to provide some motion at 50 or 59.94 or 60 Hz for sports coverage. However, interlace is prone to aliasing artifacts, both temporally (in time) and spatially (on image details). Further, interlace makes it difficult to perform transcodings, since scan lines do not sample the correct portions of the image as are required for proper transcodings to other formats. Thus, a "de-interlacer" is often used to simulate the removal of interlace before applying transcoding. Such de-interlacers are also prone to motion and picture detail artifacts and image resolution degradation.
An objective of the present invention therefore is to provide a format for images that is high quality and capable of use by any presently-used or contemplated picture rate.
Another fundamental problem of many present image formats is that they use interlace, which is a regular undersampling pattern. Such patterns are known in the art to be improper theoretical image filters, and which result in temporal and spatial artifacts through the regularity of the sampling pattern and the interaction of this pattern with natural patterns of detail in the image.
An object of the present invention, therefore, is to provide a sampling pattern that minimizes temporal and spatial artifacts.
Another object of the present invention is to provide an image format that is compatible with all the commonly used picture rates, as well as those rates expected in the future.
Moreover, any proposed image format should be usable by variety of displays to show varying degrees of quality, as appropriate for each display, from the same signal.
Thus, another objective of the present invention is to provide a distribution signal format where a variety of displays, at various levels of cost and performance, can be used when receiving the signal.
Further, the present invention allows a variety of images derived from different picture sources to be displayed individually on the same screen, or to be combined together for a composite image. The present invention thus eliminates the need for complex frame buffering normally required to provide synchronization for such simultaneous displays of images.
The present invention incorporates a method referred to herein as "pixel interlacing." The present method is referred to as pixel interlacing since it involves the extension of the concept of line interlace on a pixel-by-pixel basis.
Because pixel interlacing in the present invention does not use regular sampling patterns, the pixel interlace sampling pattern is theoretically able to avoid aliasing artifacts. Those artifacts which remain are in the form of image position irregularities in a noise-like position offset. The present pixel interlace method can be seen to be similar to the irregular manner in which film grains produce images. Such artifacts are typically quite small in the image, and are therefore unnoticed by the majority of viewers. In the present invention, position errors never exceed the size of a pixel interlace sample (a "pixel plate" as described below), and are therefore bounded in the size of the position error.